The interaction between wind-generated gravity waves and tidal currents is examined from the starting point of the gravity wave energy budget equation of Longuet-Higgins and Stewart, Equations are, developed whichIallow the variation in the short wave amplitude and wavenumber to be predicted for a linear tidal wave system having a standing wave and a progressive wave component. An additional term, unmentioned by Longuet-Higgins and Stewart, is shown to have an important role in describing the physical mechanism of the interaction and in the magnitude of the variation produced Wave data. from the North Sea is shown to exhibit this variation with the correct phase but with an amplitude variation 40% greater than predicted. A numerical model is set up to allow predictions to be computed for conditions where an analytical solution to the energy budget equation is not possible, e.g., for waves and tides in variable depths, 'Wave data from Southampton Water, under short fetch conditions, show an upward trend in wave energy when the tidal current begins to ebb and the numerical solutions are used to. show this is consistent with the wave-current',interaction. n The high variability' in wave energy between consecutive wave records in Southampton Water cannot be accounted for by this interaction theory and it is necessary to postulate the importance of other mechanisms in causing this variability.